Method and apparatus for performing random access in wireless communication system

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The present invention relates to a method and an apparatus for performing random access in a wireless communication system. More specifically, proposed is a method of, when a terminal intends to perform random access through multiple PRACH preamble transmission in an unlicensed band, determining whether to change or reset a CP length of a channel access procedure gap or a PRACH preamble according to the number of multiple PRACH preamble transmissions.

TECHNICAL FIELD

The disclosure relates to a method and device for performing randomaccess in a wireless communication system. More specifically, in awireless communication system, in particular, in a node receiving adownlink signal or a system and node that want to transmit an uplinksignal in an unlicensed band, when it is intended to perform randomaccess through transmission of multiple physical random access channel(PRACH) preambles, the disclosure relates to a method of setting achannel access procedure gap for access to an unlicensed band.

BACKGROUND ART

In order to meet the demand for wireless data traffic explosivelyincreasing due to the commercialization of 4G communication systems andthe increase in multimedia services, an improved 5G communication systemor a pre-5G communication system is being developed. For this reason, a5G communication system or a pre-5G communication system is referred toas a beyond 4G network communication system or a post LTE system.

In order to increase a data transmission rate, consideration is beinggiven to implementing the 5G communication system in a mmWave band(e.g., 60 GHz band). In order to mitigate a route loss of electronicwaves in a mmWave band and to increase transmission distances ofelectronic waves, the technologies of beamforming, massive multipleinput and output (MIMO), full dimensional MIMO (FD-MIMO), array antenna,analog beamforming, and large scale antenna have been discussed for the5G communication system.

Further, To meet the demand for wireless data traffic having increasedsince deployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access(NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

DISCLOSURE OF INVENTION Technical Problem

The disclosure relates to a method and device for performing randomaccess in a wireless communication system. In particular, an embodimentof the disclosure provides a method of determining a length of a PRACHpreamble and a channel access procedure gap in an unlicensed bandaccording to the number of PRACH preamble transmissions, whentransmitting multiple PRACH preambles in order to perform random accessin a node receiving a downlink signal in the unlicensed band or a systemand node that want to transmit an uplink signal.

Solution to Problem

According to an embodiment of the disclosure, a method performed by aterminal includes receiving configuration information for transmissionof multiple random access preambles from a base station; transmitting afirst random access preamble based on the configuration information fortransmission of the multiple random access preambles; adjusting at leastone of a length of a channel access procedure gap for a second randomaccess preamble or a length of a random access channel transmissioninterval based on transmission of the first random access preamble; andattempting channel access for transmission of the second random accesspreamble in the channel access procedure gap based on adjustment of atleast one of the length of the channel access procedure gap or thelength of the random access channel transmission interval.

According to an embodiment of the disclosure, a terminal includes atransceiver; and a controller configured to control to receiveconfiguration information for transmission of multiple random accesspreambles from a base station through the transceiver, to transmit afirst random access preamble based on the configuration information fortransmission of the multiple random access preambles through thetransceiver, to adjust at least one of a length of a channel accessprocedure gap or a length of a random access channel transmissioninterval for a second random access preamble based on transmission ofthe first random access preamble, and to attempt channel access fortransmission of the second random access preamble in the channel accessprocedure gap based on adjustment of at least one of the length of thechannel access procedure gap or the length of the random access channeltransmission interval.

According to an embodiment of the disclosure, a method performed by abase station includes transmitting configuration information fortransmission of multiple random access preambles to a terminal;receiving a first random access preamble from the terminal based on theconfiguration information for transmission of the multiple random accesspreambles; and receiving a second random access preamble from theterminal, wherein at least one of a length of a channel access proceduregap or a length of a random access channel transmission interval for thesecond random access preamble is adjusted based on transmission of thefirst random access preamble.

According to an embodiment of the disclosure, a base station includes atransceiver; and a controller configured to control to transmitconfiguration information for transmission of multiple random accesspreambles to a terminal through the transceiver, to receive a firstrandom access preamble from the terminal through the transceiver basedon the configuration information for transmission of the multiple randomaccess preambles, and to receive a second random access preamble fromthe terminal through the transceiver, wherein at least one of a lengthof a channel access procedure gap or a length of a random access channeltransmission interval for the second random access preamble is adjustedbased on transmission of the first random access preamble.

Advantageous Effects of Invention

According to an embodiment of the disclosure, a method and device forperforming random access in a wireless communication system can beprovided.

Further, according to an embodiment of the disclosure, in a wirelesscommunication system, in particular, when performing random access usingmultiple PRACH preamble transmission in a system and node that transmitand receive signals through an unlicensed band, by changing the channelaccess procedure gap using information on the number of PRACH preambletransmissions, the probability of success of random access of the systemand node is improved; thus, the unlicensed band can be used moreefficiently.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a transmission structure in time andfrequency domains of an uplink or a downlink of an NR system accordingto an embodiment of the disclosure.

FIG. 2 is a diagram illustrating a channel access procedure in anunlicensed band according to an embodiment of the disclosure.

FIG. 3 is a diagram illustrating a downlink to uplink scheduling methodand a resource region in an NR system according to an embodiment of thedisclosure.

FIG. 4 is a diagram illustrating a synchronization signal block in an NRsystem according to an embodiment of the disclosure.

FIG. 5 is a diagram illustrating an example of a contention-based accessprocedure according to an embodiment of the disclosure.

FIG. 6 is a diagram illustrating an uplink physical layer channel forrandom access according to an embodiment of the disclosure.

FIG. 7 is a diagram illustrating an example of various embodiments ofthe disclosure.

FIG. 8 is a diagram illustrating another example of various embodimentsof the disclosure.

FIG. 9 is a diagram illustrating another example of various embodimentsof the disclosure.

FIG. 10 is a flowchart illustrating an operation of a base stationaccording to various embodiments of the disclosure.

FIG. 11 is a flowchart illustrating an operation of a UE according tovarious embodiments of the disclosure.

FIG. 12 is a diagram illustrating a configuration of a base stationaccording to various embodiments of the disclosure.

FIG. 13 is a diagram illustrating a configuration of a UE according tovarious embodiments of the disclosure.

MODE FOR THE INVENTION

Hereinafter, embodiments of the disclosure will be described in detailwith reference to the accompanying drawings.

When describing an embodiment, a description of technical contents wellknown in the art of the disclosure and not directly related to thedisclosure will be omitted. This is to more clearly convey the gist ofthe disclosure without obscuring the subject matter by omittingunnecessary description.

Similarly, in the attached drawings, some components are illustrated inan exaggerated or schematic form or are omitted. Further, a size of eachcomponent does not entirely reflect an actual size. In each drawing, thesame reference numerals are assigned to the same or correspondingcomponents.

Advantages and features of the disclosure, and a method of achievingthem will be apparent with reference to the embodiments described belowin detail together with the accompanying drawings. However, thedisclosure is not limited to embodiments disclosed below, but may beimplemented in various different forms. The present embodiments enablethe complete disclosure of the disclosure and are provided to fullynotify the scope of the disclosure to those skilled in the art, and thedisclosure is defined by the scope of the claims. The same referencenumerals refer to the same components throughout the specification.

In this case, it may be understood that each block of a flowchart andcombinations of the flowchart may be performed by computer programinstructions. Because these computer program instructions may be mountedin a processor of a universal computer, a special computer, or otherprogrammable data processing equipment, the instructions performedthrough a processor of a computer or other programmable data processingequipment generate a means that performs functions described in ablock(s) of the flowchart. In order to implement a function with aspecific method, because these computer program instructions may bestored at a computer available or computer readable memory that candirect a computer or other programmable data processing equipment,instructions stored at the computer available or computer readablememory may enable to produce a production item including an instructionmeans that performs a function described in block(s) of the flowchart.Because computer program instructions may be mounted on a computer orother programmable data processing equipment, a series of operationsteps are performed on the computer or other programmable dataprocessing equipment and generate a process executed with the computer,and instructions that direct the computer or other programmable dataprocessing equipment may provide steps for executing functions describedin block(s) of the flowchart.

Further, each block may represent a portion of a module, segment, orcode including at least one executable instruction for executing aspecific logical function(s). Further, in several replaceable executionexamples, it should be noted that functions described in blocks may beperformed regardless of order. For example, two consecutivelyillustrated blocks may be substantially simultaneously performed or maybe sometimes performed in reverse order according to a correspondingfunction.

In this case, a term ‘-unit’ used in the present embodiment meanssoftware or a hardware component such as a field programmable gate array(FPGA) or an application specific integrated circuit (ASIC) and performsany function. However, “-unit” is not limited to software or hardware.“-unit” may be configured to store at a storage medium that can addressand be configured to reproduce at least one processor. Therefore,“-unit” includes, for example, components such as software components,object-oriented software components, class components, and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of a program code, drivers, firmware, microcode, circuit, data,database, data structures, tables, arrays, and variables. A functionprovided within components and “-units” may be performed by coupling thesmaller number of components and “-units” or by subdividing thecomponents and “-units” into additional components and “-units”.Further, components and “-units” may be implemented to reproduce atleast one CPU within a device or a security multimedia card. Further, inan embodiment, ‘-unit’ may include at least one processor.

A 5G system is considering supporting various services compared to theexisting 4G system. For example, the most representative services mayinclude an enhanced mobile broad band (eMBB) service, an ultra-reliableand low latency communication (URLLC) service, a massive machine typecommunication (mMTC) service, an evolved multimedia broadcast/multicastservice (eMBMS), and the like. A system providing the URLLC service maybe referred to as a URLLC system, and a system providing an eMBB servicemay be referred to as an eMBB system. Further, the terms ‘service’ and‘system’ may be used interchangeably.

In this way, in a communication system, a plurality of services may beprovided to a user, and in order to provide such a plurality of servicesto users, a method of providing each service within the same time periodaccording to characteristics and a device using the same are required.

In a wireless communication system, for example, an LTE or LTE-A system,or a 5G new radio (NR) system, by transmitting downlink controlinformation (DCI) including resource allocation information fortransmitting a downlink signal transmitted from a base station to aterminal through a physical downlink control channel (PDCCH), thewireless communication system may be configured to receive downlinksignals of at least one of downlink control information (e.g.,channel-state information reference signal (CSI-RS)), a physicalbroadcast channel ((PBCH), or a physical downlink shared channel(PDSCH)) to the terminal. For example, the base station may transmit DCIinstructing to the terminal to receive the PDSCH through the PDCCH inthe subframe n, and the terminal that has received the DCI receives thePDSCH in the subframe n according to the received downlink controlinformation. Further, in the LTE, LTE-A, or NR system, the base stationmay transmit DCI including uplink resource allocation information to theterminal through a PDCCH to set so that the terminal transmits an uplinksignal of at least one of uplink control information (e.g., a soundingreference signal (SRS), uplink control information (UCI), a physicalrandom access channel (PRACH), or a physical uplink shared channel(PUSCH)) to the base station. For example, the terminal that hasreceived uplink transmission configuration information (or uplink DCI orUL grant) transmitted from the base station through the PDCCH in asubframe n may perform uplink data channel transmission (hereinafter,PUSCH transmission) according to a predefined time (e.g., n+4), a time(e.g., n+k) set through a higher signal, or uplink signal transmissiontime indicator information (e.g., n+k) included in the uplinktransmission configuration information.

When the preset downlink transmission is transmitted from the basestation to the terminal through the unlicensed band or when the presetuplink transmission is transmitted from the terminal to the base stationthrough the unlicensed band, the transmitting device (base station orterminal) performs a channel access procedure (or listen-before talk(LBT)) for an unlicensed band in which the signal transmission isconfigured before or immediately before a preset signal transmissionstart time point, and according to the execution result of the channelaccess procedure, when it is determined that the unlicensed band is inan idle state, the transmitting device may access the unlicensed band toperform the preset signal transmission. When it is determined that theunlicensed band is not idle or occupied according to the channel accessprocedure performed by the transmitting device, the transmitting devicecannot access the unlicensed band; thus, the transmitting device cannotperform transmission of the preset signal.

In a channel access procedure in the unlicensed band configured totransmit the signal, the transmitting device may generally receive thesignal in the unlicensed band during a predetermined time or a timecalculated according to a predefined rule (e.g., a time calculatedthrough at least one random value selected by the base station or theterminal) and compare the strength of the received signal with athreshold value defined in advance or calculated by a functionconfigured with at least one variable of a channel bandwidth or abandwidth of a signal to be transmitted, strength of transmission power,a beam width of a transmission signal and the like to determine an idlestate of the unlicensed band. For example, when the strength of a signalreceived during 25 us is less than a predefined threshold value of −72dBm, the transmitting device determines that the unlicensed band is inan idle state and may transmit a preset signal. In this case, themaximum possible time of signal transmission may be limited according tothe maximum channel occupancy time defined for each country or region inthe unlicensed band, or the type of a transmission device (e.g., a basestation or a terminal, or a master device or a slave device). Forexample, in the case of Japan, in an unlicensed band of 5 GHz, byoccupying a channel without performing an additional channel accessprocedure for a maximum time of 4 ms after performing the channel accessprocedure, the base station or the terminal may transmit a signal. Whenthe strength of the signal received during 25 us is greater than apredefined threshold value −72 dBm, the base station determines that theunlicensed band is not in an idle state, and does not transmit a signal.

In the case of a 5G communication system, in order to provide variousservices and support a high data rate, various technologies such asretransmission of a code block group (CBG) unit and technology capableof transmitting an uplink signal without uplink scheduling informationhave been introduced. Therefore, in the case of performing 5Gcommunication through an unlicensed band, a more efficient channelaccess procedure in consideration of various variables is required.

The wireless communication system is evolving from an initialvoice-oriented service to a broadband wireless communication system thatprovides high-speed and high-quality packet data services as incommunication standards such as high speed packet access (HSPA), longterm evolution (LTE or evolved universal terrestrial radio access(E-UTRA)), and LTE-advanced (LTE-A) of 3GPP, high rate packet data(HRPD) of 3GPP2, ultra mobile broadband (UMB), and 802.16e of IEEE.Further, as a 5th generation wireless communication system, acommunication standard of 5G or new radio (NR) is being made.

In this way, in a wireless communication system including the 5thgeneration, at least one service of enhanced mobile broadband (eMBB),massive machine type communications (mMTC), or ultra-reliable andlow-latency communications (URLLC) may be provided to the terminal. Theservices may be provided to the same terminal during the same timeperiod. In an embodiment, eMBB may be a service for high-speedtransmission of high-capacity data, mMTC may be a service aiming atminimizing terminal power and accessing multiple terminals, and URLLCmay be a service aiming at high reliability and low latency, but theyare not limited thereto. The three services may be a major scenario inan LTE system or a system such as 5G/NR (new radio, next radio) afterLTE.

When the base station schedules data corresponding to the eMBB serviceto a certain terminal in a specific transmission time interval (TTI), ifa situation occurs in which URLLC data should be transmitted in the TTI,in a frequency band in which the eMBB data is already scheduled andbeing transmitted, the base station may not transmit a part of the eMBBdata, but may transmit the generated URLLC data in the frequency band.The terminal in which eMBB data is scheduled and the terminal in whichURLLC data is scheduled may be the same terminal or different terminals.In such a case, because a part of the eMBB data that has already beenscheduled and being transmitted may not be transmitted, the possibilityof damage in the eMBB data increases. Therefore, in the above case, itis necessary to determine a method in which a terminal in which eMBBdata is scheduled or a terminal in which URLLC data is scheduledprocesses a received signal and a method of receiving a signal.

Terms to be described later are terms defined in consideration offunctions in the disclosure, which may vary according to the intentionor custom of users or operators. Therefore, the definition should bemade based on the contents throughout the present specification.Hereinafter, the base station is a subject that performs resourceallocation of the terminal, and may be at least one of an enode B (eNB),a node B, a base station (BS), a gNB, a radio access unit, a basestation controller, or a node on a network. The terminal may include auser equipment (UE), a mobile station (MS), a cellular phone, a smartphone, a computer, a vehicle, or a multimedia system capable ofperforming a communication function. In the disclosure, a downlink (DL)refers to a radio transmission path of a signal transmitted from a basestation to a terminal, and an uplink (UL) refers to a radio transmissionpath of a signal transmitted from the terminal to the base station.Further, hereinafter, an embodiment of the disclosure will be describedusing an LTE or LTE-A system as an example, but the embodiment of thedisclosure may be applied to other communication systems having asimilar technical background or channel type. For example, 5G mobilecommunication technology (5G, new radio, NR) developed after LTE-A maybe included therein. Further, the embodiments of the disclosure may beapplied to other communication systems through some modificationswithout significantly departing from the scope of the disclosure, asdetermined by a person having skilled technical knowledge.

As a representative example of the broadband wireless communicationsystem, in the NR system, the downlink (DL) employs an orthogonalfrequency division multiplexing (OFDM) scheme, and the uplink (UL)employs OFDM and single carrier frequency division multiple access(SC-FDMA) scheme. The uplink refers to a radio link in which theterminal transmits data or control signals to the base station, and thedownlink refers to a radio link in which the base station transmits dataor control signals to the terminal. In the multiple access scheme asabove described, it is possible to distinguish data or controlinformation of each user by allocating and operating time-frequencyresources to carry data or control information for each user so thatthey do not overlap with each other, that is, orthogonality isestablished.

When a decoding failure occurs in initial transmission, the NR systememploys a hybrid automatic repeat request (HARQ) scheme in which aphysical layer retransmits the corresponding data. In the HARQ scheme,when a receiver fails to accurately decode data, the receiver transmitsnegative acknowledgement (NACK) notifying a transmitter of the decodingfailure so that the transmitter may retransmit the corresponding data inthe physical layer. By combining the data retransmitted by thetransmitter with data in which decoding has been previously failed, thereceiver improves a data reception performance. Further, when thereceiver correctly decodes data, the receiver may transmitacknowledgement (ACK) notifying the transmitter of decoding success toenable the transmitter to transmit new data.

FIG. 1 is a diagram illustrating a basic structure of a time-frequencydomain, which is a radio resource domain in which the data or controlchannel is transmitted in an uplink/downlink of an NR system or asimilar system according to an embodiment of the disclosure.

Referring to FIG. 1, a horizontal axis represents a time domain resourceand a vertical axis represents a frequency domain resource. A minimumtransmission unit in the time domain resource is an OFDM to DFT-s-OFDMsymbol, and the N_(symb) number of OFDM to DFT-s-OFDM symbols 101 aregathered to form one slot 102. Here, the OFDM symbol is a symbol of acase of transmitting and receiving a signal using an OFDM multiplexingmethod, and the DFT-s-OFDM symbol is a symbol of a case of transmittingand receiving a signal using a DFT-s-OFDM or SC-FDMA multiplexingmethod. Hereinafter, in various embodiments of the disclosure, forconvenience of description, OFDM and DFT-s-OFDM symbols will be commonlydescribed as OFDM symbols without distinction of a symbol, and will bedescribed based on downlink signal transmission and reception, but theywill be applicable to uplink signal transmission and reception.

When an interval between subcarriers is 15 kHz, one slot is gathered toform one subframe 103, and each of lengths of the slots and subframes is1 ms. In this case, the number and length of slots constituting onesubframe 103 may be different according to the interval betweensubcarriers. For example, when the interval between subcarriers is 30kHz, two slots may be gathered to form one subframe 103. In this case,the length of the slot is 0.5 ms and the length of the subframe is 1 ms.A radio frame 104 is a time domain resource section configured with 10subframes. A minimum transmission unit in the frequency domain resourceis a subcarrier, and a bandwidth of an entire system transmission bandis configured with the total N_(sc) ^(BW) number of subcarriers 105.However, such specific numerical values may be applied variably. Forexample, in the case of the LTE system, the interval between subcarriersis 15 kHz, but two slots are gathered to form one subframe 103, and inthis case, the length of the slot is 0.5 ms and the length of thesubframe is 1 ms.

A basic unit of a resource in the time-frequency domain resource is aresource element (RE) 106, which may be represented by an OFDM symbolindex and a subcarrier index. A resource block ((RB) or physicalresource block (PRB)) 107 may be defined as the N_(symb) number ofconsecutive OFDM symbols 101 in the time domain resource and the N_(sc)^(RB) number of consecutive subcarriers 108 in the frequency domainresource. Therefore, one RB 107 in one slot may include the N_(symb)XN_(SC) ^(RB) number of REs. In general, the minimum allocation unit inthe frequency domain resource of data is the RB 107. In an NR system, ingeneral, N_(symb)=14 and N_(SC) ^(RB)=12, and the number (N_(RB)) of RBsmay vary according to the bandwidth of the system transmission band. Inthe LTE system, in general, the N_(symb)=7 and N_(SC) ^(RB)=12, and theN_(RB) may vary according to the bandwidth of the system transmissionband.

Downlink control information may be transmitted within the first Nnumber of OFDM symbols in the subframe. In general, N may be {1, 2, 3},and the UE may receive the number of symbols in which the downlinkcontrol information may be transmitted from the base station through ahigher signal. Further, according to an amount of control information tobe transmitted in a current slot, the base station may vary the numberof symbols in which downlink control information may be transmitted inthe slot for each slot, and transmit information on the number ofsymbols to the UE through a separate downlink control channel.

In the NR to LTE system, scheduling information on downlink data oruplink data may be transmitted from the base station to the UE throughdownlink control information (DCI). DCI is defined according to variousformats and may represent whether it is scheduling information (ULgrant) for uplink data or scheduling information (DL grant) for downlinkdata according to each format, and whether it is compact DCI with asmall size of control information, whether the control information isfall-back DCI, whether spatial multiplexing using multiple antennas isapplied, whether it is DCI for power control, and the like. For example,a DCI format (e.g., DCI format 1_0 of NR), which is scheduling controlinformation (DL grant) on downlink data may include at least one of thefollowing control information.

-   -   DCI format identifier: Identifier that identifies a format of        the received DCI    -   Frequency domain resource assignment: indicate an RB assigned to        data transmission.    -   Time domain resource assignment: indicate slots and symbols        assigned to data transmission.    -   VRB-to-PRB mapping: indicate whether to apply a VRB mapping        method    -   Modulation and coding scheme (MCS): indicate a modulation method        used for data transmission and a size of a transport block,        which is data to be transmitted.    -   New data indicator: indicate whether HARQ initial transmission        or retransmission.    -   Redundancy version: indicate a redundancy version of HARQ.    -   HARQ process number: indicate the process number of HARQ.    -   PDSCH allocation information (Downlink assignment index):        indicate the number (e.g., HARQ-ACK number) of PDSCH reception        results to be reported to the base station to the UE    -   Transmit power control (TPC) command for a physical uplink        control channel (PUCCH): indicate a transmit power control        command for a PUCCH, which is an uplink control channel.    -   PUCCH resource indicator: indicate a PUCCH resource used for        HARQ-ACK report including a reception result for a PDSCH set        through the corresponding DCI    -   PUCCH transmission timing indicator (PDSCH-to-HARQ_feedback        timing indicator): indicate slot or symbol information in which        a PUCCH for HARQ-ACK report including a reception result for the        PDSCH set through the corresponding DCI should be transmitted

The DCI may be transmitted on an enhanced PDCCH (EPDCCH) (or enhancedcontrol information, hereinafter, it is used interchangeably) or aphysical downlink control channel (PDCCH) (or control information,hereinafter, it is used interchangeably), which is a downlink physicalcontrol channel through channel coding and modulation processes.

In general, the DCI is scrambled with a specific radio network temporaryidentifier (RNTI) (or UE identifier C-RNTI) independently for each UE toadd a cyclic redundancy check (CRC), and is configured with eachindependent PDCCH and transmitted after channel coding. In the timedomain resource, the PDCCH is mapped and transmitted during the controlchannel transmission interval. A frequency domain resource mappingposition of the PDCCH may be determined by an identifier (ID) of eachUE, and be spread in the entire system transmission band andtransmitted.

Downlink data may be transmitted on a physical downlink shared channel(PDSCH), which is a physical channel for downlink data transmission. ThePDSCH may be transmitted after the control channel transmissioninterval, and scheduling information such as a specific mapping positionand modulation scheme in the frequency domain resource is determinedbased on the DCI transmitted through the PDCCH.

The base station notifies the UE of a modulation scheme applied to thePDSCH to be transmitted to the UE and a size (transport block size(TBS)) of data to be transmitted through the MCS among the controlinformation constituting the DCI. In an embodiment, the MCS may beconfigured with 5 bits or more or less bits. The TBS corresponds to asize before channel coding for error correction is applied to data(transport block (TB)) to be transmitted by the base station.

Modulation methods supported by the NR system are quadrature phase shiftkeying (QPSK), quadrature amplitude modulation (16QAM), 64QAM, and256QAM, and each modulation order (Qm) thereof is 2, 4, and 6. That is,in the case of QPSK modulation, 2 bits per symbol may be transmitted, inthe case of 16QAM modulation, 4 bits per symbol may be transmitted, inthe case of 64QAM modulation, 6 bits per symbol may be transmitted, andin the case of 256QAM modulation, 8 bits per symbol may be transmitted.Further, a modulation scheme of 256QAM or more may be used according tosystem modifications.

In the NR system, the uplink/downlink HARQ employs an asynchronous HARQscheme in which a data retransmission time point is not fixed. Whendescribing the downlink as an example, when HARQ NACK feedback isreceived from the UE for initial transmission data transmitted by thebase station, the base station freely determines a transmission timepoint of retransmission data by a scheduling operation. For a HARQoperation, the UE may buffer data determined to an error as a decodingresult of received data, and then perform combining with dataretransmitted from the base station. HARQ ACK/NACK information of aPDSCH transmitted in a subframe n-k may be transmitted from the UE tothe base station through a PUCCH or PUSCH in a subframe n. In the caseof a 5G communication system such as NR, the k value may be included andtransmitted in the DCI instructing or scheduling reception of the PDSCHtransmitted in the subframe n-k, or the k value may be configure to theUE through a higher signal. In this case, the base station may configureone or more k values as higher signals and indicate a specific k valuethrough the DCI. In this case, the k may be determined according to aHARQ-ACK processing capability of the UE, that is, the minimum timerequired for the UE to receive the PDSCH and to generate and reportHARQ-ACK for the PDSCH. Further, the UE may use a predefined value or adefault value until the k value is configured.

Although the description of the wireless communication system and themethod and device proposed in the embodiment of the disclosure have beendescribed based on the NR system, the contents of the disclosure are notlimited to the NR system, but may be applied to various wirelesscommunication systems such as LTE, LTE-A, and LTE-A-Pro and 5G. Further,the contents of the disclosure are described based on a system and adevice for transmitting and receiving signals using an unlicensed band,but the contents of the disclosure may be applied to a system operatingin a licensed band.

Hereinafter, in the disclosure, higher layer signaling or a highersignal is a signal transmission method transmitted from the base stationto the UE using a downlink data channel of the physical layer or fromthe UE to the base station using an uplink data channel of the physicallayer and includes a signal transmission method transmitted throughradio resource control (RRC) signaling, packet data convergence protocol(PDCP) signaling, or a medium access control (MAC) control element (MACCE). Further, system information, for example, a system informationblock (SIB) commonly transmitted to a plurality of UEs may be includedin the higher signaling or higher signal.

In the case of a system that performs communication in an unlicensedband, a transmitting device (base station or UE) that wants to transmita signal through the unlicensed band performs a channel access procedure(or listen-before talk (LBT)) for the unlicensed band to perform thecommunication before transmitting the signal, and when it is determinedthat the unlicensed band is in an idle state according to the channelaccess procedure, the transmitting device may access the unlicensed bandto perform signal transmission. When it is determined that theunlicensed band is not in an idle state according to the performedchannel access procedure, the transmitting device may not perform signaltransmission.

More specifically, when an base station or a UE wants to transmit adownlink or uplink signal in an unlicensed band, a channel accessprocedure that can be performed by the base station or UE may bedescribed by classifying into at least the following types.

-   -   Type 1: Uplink/downlink signal transmission after performing a        channel access procedure for a variable time    -   Type 2: Uplink/downlink signal transmission after performing a        channel access procedure for a fixed time    -   Type 3: Downlink or uplink signal transmission without        performing a channel access procedure

Hereinafter, in various embodiments of the disclosure, a case in whichthe base station transmits a downlink signal to the UE through anunlicensed band and a case in which the UE transmits an uplink signal tothe base station through an unlicensed band will be described together,but the content proposed in various embodiments of the disclosure may beapplied in the same manner or with partially modified to the case inwhich the UE transmits an uplink signal to the base station through anunlicensed band or the case in which the base station transmits adownlink signal to the UE through an unlicensed band. Therefore, adetailed description of transmission and reception of downlink signalswill be omitted. Further, in various embodiments of the disclosure, itis assumed that one downlink data information (codeword or TB) or uplinkdata information is transmitted and received between the base stationand the UE. However, the content proposed in the disclosure may beapplied to even the case in which the base station transmits a downlinksignal to a plurality of UEs or the case in which a plurality ofcodewords or TBs are transmitted and received between the base stationand the UE.

A transmitting node (hereinafter, base station or UE) that wants totransmit signals in an unlicensed band may determine a channel accessprocedure method according to the type of signal to be transmitted. Forexample, when the base station wants to transmit a downlink signalincluding a downlink data channel in an unlicensed band, the basestation may perform a type 1 channel access procedure. When the basestation wants to transmit a downlink signal, for example, asynchronization signal or a downlink control channel that does notinclude a downlink data channel in an unlicensed band, the base stationmay perform a type 2 channel access procedure and transmit the downlinksignal.

In this case, the channel access procedure method may be determinedaccording to a transmission length of a signal to be transmitted in anunlicensed band or a length of a time or interval used by occupying theunlicensed band. In general, the type 1 method may have to perform thechannel access procedure for a longer time than that when performing thechannel access procedure with the type 2 method. Accordingly, when asignal is to be transmitted during a short time period or a time of areference time (e.g., Xms or Y symbol) or less, a type 2 channel accessprocedure may be performed. However, when a signal is to be transmittedduring a long time period or a time of a reference time (e.g., Xms or Ysymbol) or more, a type 1 channel access procedure may be performed. Inother words, different type channel access procedures may be performedaccording to a use time of the unlicensed band.

When a type 1 channel access procedure is performed according to atleast one of the above criteria, a channel access priority class may bedetermined according to a quality of service class identifier (QCI) ofthe signal to be transmitted in the unlicensed band, and a channelaccess procedure may be performed using at least one of predefined setupvalues, as illustrated in Table 1 for the determined channel accesspriority class. For example, each of QCI 1, 2, and 4 denotes QCI valuesfor services such as conversational voice, conversational video (livestreaming), and non-conversational video (buffered streaming). When asignal for a service that does not match to the QCI of Table 1 is to betransmitted to the unlicensed band, the QCI closest to the QCI of Table1 and the service may be selected, and a channel access priority classfor the QCI may be selected.

Table 1 represents the mapping relationship between channel accesspriority classes and QCI.

TABLE 1 Channel Access Priority QCI 1 1, 3, 5, 65, 66, 69, 70 2 2, 7 34, 6, 8, 9 4 —

Defer duration according to the determined channel access priority (p),a set (CW_p) of contention window values or sizes, minimum and maximumvalues (CW_min,p, CW_max,p) of contention window, or the maximum channeloccupancy possible period (T_mcot,p), and the like may be determinedthrough Table 2. In other words, an base station that wants to transmita downlink signal in the unlicensed band performs a channel accessprocedure for the unlicensed band for a minimum T_f+m_p*T_sl time. T_frepresents a fixed sensing length value (e.g., 16 us), and T_slrepresents a sensing slot length (e.g., 9 us). Further, m_p isdetermined according to the priority class. When a channel accessprocedure is to be performed with a channel access priority class 3(p=3), for a size T_f+m_p*T_sl of the defer duration required to performthe channel access procedure, the size thereof is set using m_p=3. Whenit is determined that the unlicensed band is in an idle state in all ofthe m_p*T_sl times, N=N−1 may be obtained. In this case, N is selectedas an arbitrary integer value among values between 0 and a value (CW_p)of contention window at a time point that performs the channel accessprocedure. In the case of channel access priority class 3, a minimumcontention window value and a maximum contention window value are 15 and63, respectively. When it is determined that the unlicensed band is inan idle state in the defer duration and an additional channel accessprocedure execution gap, the base station may transmit a signal throughthe unlicensed band for a T_mcot,p time (8 ms). Table 2 illustrates achannel access priority class in the downlink. For convenience ofdescription, the disclosure will be described using a downlink channelaccess priority class, but in the case of uplink, the channel accesspriority class in Table 2 may be reused or a channel access priorityclass for uplink transmission may be defined and used.

TABLE 2 Channel Access Priority Class allowed (p) m_(p) CW_(min,p)CW_(max,p) T_(mcot,p) CW_(p) sizes 1 1  3   7 2 ms {3, 7} 2 1  7  15 3ms {7, 15} 3 3 15  63 8 or 10 ms {15, 31, 63} 4 7 15 1023 8 or 10 ms{15, 31, 63, 127, 255, 511, 1023}

An initial contention window value (CW_p) is a minimum value (CW_min,p)of the contention window. The base station that selects the N value mayperform a channel access procedure in a T_sl period, and when it isdetermined that the unlicensed band is in an idle state through thechannel access procedure performed in the T_sl period, the base stationmay change a value to N=N−1, and when N=0, the base station may transmitthe signal through the unlicensed band for a maximum T_mcot,p time. Whenthe unlicensed band determined through the channel access procedure atthe time T_sl is not in an idle state, the channel access procedure maybe performed again without changing the N value.

The value of the contention window (CW_p) may be changed based on thereception result for the downlink data channel in a reference subframeor a reference slot in the downlink signal transmission interval (orMCOT) in which the base station transmits most recently through theunlicensed band at or immediately before a time point at which the basestation initiates a channel access procedure or a time point at whichthe base station selects the N value to perform the channel accessprocedure. In other words, the base station may receive the receptionresults of the UE for downlink data transmitted in the referencesubframe or the reference slot and increase or minimize a size of CW_paccording to a ratio (Z) of NACK among the received reception results.

Referring to FIG. 2, for example, at or immediately before a time point270 at which the base station initiates a channel access procedure or atime point at which the base station selects the N value to perform achannel access procedure, a first transmission interval 240(hereinafter, the first slot to the first subframe) of a downlink signaltransmission interval 230 transmitted most recently through theunlicensed band becomes a contention window change reference slot forthe channel access procedure 270. When the base station cannot receivethe reception result for a downlink data channel transmitted in thefirst slot 240 of the transmission interval 230, for example, when atime interval between the first subframe 240 and a time point 270 atwhich the base station initiates a channel access procedure is n slotsor subframes or less, that is, when the base station initiates a channelaccess procedure before a time in which the UE may report the downlinkdata channel reception result for the first subframe 240, the firstsubframe 240 of the most recent downlink signal transmission intervaltransmitted before the downlink signal transmission interval 230 becomesa reference subframe. In other words, at a time point 270 in which thebase station initiates the channel access procedure or at or immediatelybefore a time point in which the base station selects the N value toperform the channel access procedure, when the base station does notreceive the reception result of downlink data transmitted in thereference subframe from the UE, the base station may determine the firstsubframe of the most recently transmitted downlink signal transmissioninterval among the reception results for the downlink data channelpreviously received from the UEs as the reference subframe. The basestation may determine the contention window size used in the channelaccess procedure 270 using the downlink data reception result receivedfrom the UEs for the downlink data transmitted through the downlink datachannel in the reference subframe.

For example, when 80% or more of the reception results of the UE fordownlink data transmitted to the UE through the downlink data channel inthe first subframe 240 are determined to NACK among downlink signalstransmitted through the unlicensed band, the base station that hastransmitted a downlink signal through a channel access procedure (e.g.,CW_p=15) set through a channel access priority class 3 (p=3) mayincrease the contention window from an initial value (CW_p=15) to a nextcontention window value (CW_p=31).

When 80% or more of the reception result of the UE is not determined toNACK, the base station may maintain a value of the contention window tothe existing value or change a value of the contention window to aninitial value of the contention window. In this case, the change of thecontention window may be commonly applied to all channel access priorityclasses or may be applied only to the channel access priority class usedin the channel access procedure. In this case, in a reference subframeor a reference slot for determining the contention window size change, amethod of determining a reception result effective in determining thesize of a contention window, that is, a method of determining a Z valueamong the reception results for the downlink data transmitted orreported by the UE to the base station for downlink data transmittedthrough a downlink data channel is as follows.

When the base station transmits one or more codewords or TB to one ormore UEs in the reference subframe or the reference slot, the basestation may determine the Z value by a ratio of NACK among receptionresults transmitted or reported by the UE for the TB received in thereference subframe or the reference slot. For example, when twocodewords or two TBs are transmitted to one UE in the reference subframeor the reference slot, the base station receives transmission or reportof a reception result of downlink data signals for the two TBs from theUE. When the NACK ratio (Z) among the two reception results is equal toor greater than a threshold value (e.g., Z=80%) defined in advance orset between the base station and the UE, the base station may change orincrease the contention window size.

In this case, when the UE bundles the downlink data reception result forone or more subframes (e.g., the M number of subframes) including thereference subframe or slot and transmits or reports the downlink datareception result to the base station, the base station may determinethat the UE has transmitted the M number of reception results. The basestation may determine the Z value with a ratio of NACK among the Mnumber of reception results and change, maintain, or initialize thecontention window size.

When the reference subframe is a reception result for a second slotamong two slots constituting one subframe, the base station maydetermine the Z value with a ratio of NACK among the reception resultsin which the UE transmits or reports to the base station for downlinkdata received in the reference subframe (i.e., second slot) and the nextsubframe.

Further, when scheduling information or downlink control information ona downlink data channel transmitted by the base station is transmittedin the same cell or frequency band as a cell or frequency band in whichthe downlink data channel is transmitted or when scheduling informationor downlink control information on a downlink data channel transmittedby the base station is transmitted through an unlicensed band, but istransmitted in a different frequency or a cell different from the cellin which the downlink data channel is transmitted, when it is determinedthat the UE is not transmitted the reception result for the downlinkdata received in the reference subframe or the reference frame and whenit is determined to DTX, NACK/DTX, or any state among the receptionresults for the downlink data transmitted by the UE, the base stationmay determine the reception result of the UE to NACK to determine the Zvalue.

Further, when scheduling information or downlink control information ona downlink data channel transmitted by the base station is transmittedthrough a licensed band, if it is determined to DTX, or NACK/DTX, or anystate among the reception results for the downlink data transmitted bythe UE, the base station may not include the reception result of the UEin the reference value Z of the contention window variation. In otherwords, the base station may ignore the reception result of the UE anddetermine the Z value.

Further, when the base station transmits scheduling information ordownlink control information on a downlink data channel through alicensed band, if the base station does not actually transmit downlinkdata (no transmission) among the downlink data reception results for thereference subframe or the reference slot transmitted or reported by theUE to the base station, the base station may ignore the reception resulttransmitted or reported by the UE for the downlink data and determinethe Z value.

In the 5G system, it is necessary to flexibly define and operate a framestructure in consideration of various services and requirements. As anexample, it may be considered that each service has different subcarrierspacing according to requirements. In the current 5G communicationsystem, a method of supporting a plurality of subcarrier spacing may bedetermined using Equation 1 as follows.

f=f ₀2^(m)  [Equation 1]

Here, f₀ denotes basic subcarrier spacing of the system, and m denotesan integer scaling factor. For example, when f₀ is 15 kHz, a set ofsubcarrier spacing that may have by a 5G communication system may beconfigured with 3.75 kHz, 7.5 kHz, 15 kHz, 30 kHz, 60 kHz, 120 kHz, 240kHz, 480 kHz, and the like. A usable subcarrier spacing set may bedifferent according to a frequency band. For example, 3.75 kHz, 7.5 kHz,15 kHz, 30 kHz, and 60 kHz may be used in a frequency band of 6 GHz orless, and 60 kHz, 120 kHz, and 240 kHz may be used in a frequency bandof 6 GHz or more.

A length of the OFDM symbol may vary according to the subcarrier spacingconstituting the OFDM symbol. This is because the subcarrier spacing andthe length of the OFDM symbol have an inverse relationship with eachother as a characteristic of the OFDM symbol. For example, when thesubcarrier spacing is doubled, the symbol length is reduced to ½, andconversely, when the subcarrier spacing is reduced to ½, the symbollength is doubled.

Hereinafter, a resource region through which a data channel istransmitted in a 5G communication system will be described.

FIG. 3 is a diagram illustrating a resource region through which a datachannel is transmitted in a 5G communication system according to anembodiment of the disclosure.

The UE monitors or searches for a PDCCH 310 in a downlink controlchannel region (hereinafter, control resource set (CORESET) to searchspace (SS)) set through a higher signal from the base station. In thiscase, the downlink control channel region is configured with time domainresource 314 and frequency domain resource 312 information, the timedomain resource 314 information may be configured in units of a symbol,and the frequency domain resource 312 information may be configured inunits of an RB or an RB group. When the UE detects the PDCCH 310 in aslot i, 300, the UE obtains downlink control information (DCI)transmitted through the detected PDCCH 310. Through the receiveddownlink control information (DCI), the UE may obtain schedulinginformation on a downlink data channel or an uplink data channel. Inother words, the DCI may include at least information on a resourceregion (or PDSCH transmission region) in which the UE should receive adownlink data channel (hereinafter, PDSCH) transmitted from the basestation or resource region information in which the UE is allocated fromthe base station for transmission of an uplink data channel (PUSCH).

A case in which the UE is scheduled to transmit an uplink data channel(PUSCH) will be described as an example as follows. The UE that hasreceived the DCI may obtain a slot index or offset information (K) toreceive a PUSCH through DCI, and determine a PUSCH transmission slotindex. For example, the UE may determine that it has been scheduled totransmit the PUSCH in a slot i+K, 305 through the received offsetinformation K based on the slot index i, 300 that receives the PDCCH310. In this case, the UE may determine a PUSCH start symbol or time inthe slot i+K, 305 or the slot i+K through the received offsetinformation K based on a CORESET received the PDCCH 310. Further, the UEmay obtain information on a PUSCH transmission time-frequency domainresource 340 in the PUSCH transmission slot 305 in the DCI. In thiscase, PUSCH transmission frequency domain resource information 330 maybe information of a PRB to a PRB group unit. The PUSCH transmissionfrequency domain resource information 330 is a domain included in aninitial uplink bandwidth (initial uplink BW) 335 or an initial uplinkbandwidth part (initial uplink BWP) determined or configured by the UEthrough an initial access procedure. When the UE receives an uplinkbandwidth or an uplink bandwidth part through a higher signal, the PUSCHtransmission frequency domain resource information 330 is a regionincluded in an uplink bandwidth or an uplink bandwidth part configuredthrough the higher signal.

PUSCH transmission time resource region information 325 may beinformation of a symbol or a symbol group unit or informationrepresenting absolute time information. In this case, the PUSCHtransmission time resource region information 325 may be representedwith a combination of a PUSCH transmission start time or symbol and alength of a PUSCH or a PUSCH end time or symbol to be included in theDCI as one field or value. In this case, the PUSCH transmission timeresource region information 325 may be included in the DCI as a field orvalue representing each of the PUSCH transmission start time or symboland the length of the PUSCH or the PUSCH end time or symbol. The UE maytransmit a PUSCH in the PUSCH transmission resource region 340determined through the DCI.

In a wireless communication system, in order to form a radio link withthe base station, the UE goes through an initial access step as follows.First, in order to access a cell in the network, the UE performs a cellsearch for obtaining synchronization with the cell in the network andobtains a master information block (MIB) through PBCH decoding. The MIBincludes the most basic information for accessing the system. Based onthe information, the UE decodes the PDCCH and the PDSCH to obtain anSIB. Thereafter, through a random access step, the UE exchanges anidentity with the base station and performs initial access to thenetwork through steps such as registration and authentication.

Hereinafter, a cell initial access operation procedure of a 5G wirelesscommunication system will be described in more detail with reference tothe drawings.

FIG. 4 is a diagram illustrating a synchronization signal (SS)/PBCHblock 400 considering in a 5G communication system according to anembodiment of the disclosure.

The SS/PBCH block 400 is configured with a primary synchronizationsignal (PSS) 401, a secondary synchronization signal (SSS) 403, and aPBCH 402.

The PSS 401 and the SSS 403 may be transmitted to 12 RBs 405 at thefrequency axis and 1 OFDM symbol 404 at the time axis. In 5G, total 1008different cell IDs may be defined, the PSS 401 may have three differentvalues according to a physical layer ID of the cell, and the SSS 403 mayhave 336 different values. The UE may know one of 1008 cell IDs as thecombination thereof through detection of the PSS 401 and the SSS 403.This may be represented by Equation 2.

N _(ID) ^(cell)=3N _(ID) ⁽¹⁾ +N _(ID) ⁽²⁾  [Equation 2]

N⁽²⁾ _(ID) may be estimated from the SSS 403 and has a value between 0and 335. N⁽¹⁾ _(ID) may be estimated from the PSS 401 and has a valuebetween 0 and 2. An N^(cell) _(ID) value, which is a cell ID, may beestimated by a combination of N⁽¹⁾ _(ID) and N⁽²⁾ _(ID).

The PBCH 402 may be transmitted to 24 RBs 406 at the frequency axis and2 OFDM symbols 404 at the time axis. In the PBCH 402, various systeminformation called MIBs may be transmitted, and included contents are asfollows.

systemFrameNumber subCarrierSpacingCommon ssb-SubcarrierOffsetdmrs-TypeA-Position pdcch-ConfigSIB1 cellBarred intraFreqReselectionspare

As described above, the SS block 400 is configured with the PSS 401, theSSS 403, and the PBCH 402, and is mapped to total 4 OFDM symbols at thetime axis. Because sizes of a transmission bandwidth 405 of the PSS 401and the SSS 403 configured with 12 RBs and a transmission bandwidth 406of the PBCH 402 configured with 24 RBs are different, within thetransmission bandwidth 406 of the PBCH 402, in the OFDM symbol in whichthe PSS 401 and the SSS 403 are transmitted, while the PSS 401 and theSSS 403 are transmitted, 6 RBs exist at both sides (corresponding to 407and 408 in FIG. 4) except 12 RBs, and resource regions corresponding toreference numerals 407 and 408 may be used for transmitting othersignals or may be empty.

All of the synchronization signal blocks may be transmitted with thesame analog beam. That is, all of the PSS 401, the SSS 403, and the PBCH402 may be transmitted with the same beam. Because an analog beam hascharacteristics that cannot be applied to the frequency axis, the sameanalog beam is applied to all frequency axis RBs within a specific OFDMsymbol to which a specific analog beam is applied. That is, all fourOFDM symbols through which the PSS 401, the SSS 403, and the PBCH 402are transmitted may be transmitted with the same analog beam.

After decoding the PDCCH and the PDSCH based on system informationincluded in the received MIB, the UE may obtain an SIB, and the SIBincludes at least an uplink cell bandwidth, a random access parameter, apaging parameter, and parameters related to an uplink power control, andthe like. The UE may form a radio link with the network through a randomaccess process based on system information and synchronization with thenetwork obtained in a search process of the cell. Random access may usea contention-based or contention-free method. When cell selection andreselection are performed in an initial access step of the cell, forpurposes such as when moving from an RRC_IDLE state to RRC_CONNECTED, acontention-based access method may be used. Contention-free randomaccess may be used in case that downlink data arrives, in case ofhandover, in case of location measurement, or in case of resettinguplink synchronization.

FIG. 5 is a diagram illustrating a contention-based access process in anNR system according to an embodiment of the disclosure. Referring toFIG. 5, a random access process is configured with a procedure of foursteps. First, in step 501, the UE transmits a random access preample sothat the base station may estimate the transmission timing of the UE.The random access preamble is transmitted through an uplink physicallayer channel corresponding to a PRACH, and a detailed descriptionthereof will be described later. Through step 501 of transmitting therandom access preamble, the base station may recognize that there is arandom access attempt and estimate a delay time between the UE and thebase station to adjust the uplink transmission timing.

In second step 502, the base station transmits a random access response(RAR) to the detected random access attempt to the UE. The RAR istransmitted through a PDSCH and includes the following message.

-   -   Random access preamble sequence index detected by the network    -   Temporary cell radio network temporary identifier (TC-RNTI)    -   Uplink scheduling grant    -   Timing advance value

The UE that has transmitted the preamble monitors a PDCCH for the RARwithin a preset time. Frequency domain resource control information onthe PDSCH through which the RAR is transmitted may be obtained from DCItransmitted to a common search space of a PDCCH set to a random accessradio network temporary identifier (RA-RNTI). The UE that has receivedthe RAR adjusts uplink transmission timing and proceeds to the nextstep.

In third step 503, the UE transmits an L2/L3 message for an RRCconnection request to the base station. The UE may transmit a messagesuch as an ID or HARQ of the UE using uplink physical layer resourcesallocated in the random access response in the second step 502. In thiscase, a message is transmitted through a PUSCH, which is an uplinkphysical channel set to TC-RNTI.

In fourth step 504, the UE receives a downlink message for contentionresolution and RRC connection setup from the base station. Thecontention resolution message is transmitted through the PDSCH, andscheduling information on the corresponding PDSCH may be obtained fromDCI transmitted to the PDCCH set to C-RNTI.

In a contention-free random access process, because contentionresolution is not required, only the first step 501 and the second step502 are used in FIG. 5.

FIG. 6 is a diagram illustrating an uplink physical layer channel usedin a random access process in NR according to an embodiment of thedisclosure.

As described above, in a first step of the random access process, the UEmay transmit a random access preamble from a PUSCH 602 using a PRACH601. Each cell has 64 available preamble sequences, and 4 long preambleformats and 9 short preamble formats may be used according to atransmission type. The UE generates 64 preamble sequences using a rootsequence index and a cyclic shift value signaled by system information,and randomly selects one sequence and uses the one sequence as apreamble.

A network may notify the UE of which time-frequency resource may be usedfor a PRACH using SIB or higher layer signaling. A frequency resourceindicates a start RB point of transmission to the UE, and the number ofuse RBs is determined according to a preamble format and appliedsubcarrier spacing. The time resource may notify preset PRACH duration,a subframe index including a PRACH occasion and a start symbol, and thenumber of PRACH occasions in a slot through a PRACH configuration index(0 to 255), as illustrated in Table 3.

TABLE 3 PRACH configuration Preamble

 mod x = y Subframe Starting Number of PRACH number of time-domain PRACHPRACH Index format x y number symbol slots within a subframe occasionswithin a PRACH slot duration 0 0 16 1 1 0 — — 0 1 0 16 1 4 0 — — 0 2 016 1 7 0 — — 0 3 0 16 1 9 0 — — 0 4 0 8 1 1 0 — — 0 5 0 8 1 4 0 — — 0 60 8 1 7 0 — — 0 7 0 8 1 9 0 — — 0 8 0 4 1 1 0 — — 0 9 0 4 1 4 0 — — 0 100 4 1 7 0 — — 0 . . . . . . 251 C 1 0 2, 7 0 2 2 6 252 C2 1 0 1, 4, 7 02 2 6 253 C2 1 0 0, 2, 4, 6, 8 0 2 2 6 254 C2 1 0 0, 1, 2, 3, 4, 0 2 2 65, 6, 7, 8, 9 255 C2 1 0 1, 3, 5, 7, 9 0 2 2 6

indicates data missing or illegible when filed

When attempting a random access procedure in an unlicensed band, inorder to transmit a PRACH preamble at a PRACH occasion, the UE shouldperform a channel access procedure. When it is determined that theunlicensed band is in an idle state according to the execution result ofthe channel access procedure, the UE may access the unlicensed band totransmit the preamble. However, when the unlicensed band is not in anidle state, the UE cannot transmit the preamble; thus, the probabilityof success of the random access procedure decreases. Accordingly, in a5G communication system, in order to overcome deterioration of thesuccess probability of random access due to the failure of the channelaccess procedure, transmission of multiple PRACH preambles at a PRACHoccasion may be considered. When one UE transmits multiple PRACHpreambles in the unlicensed band, a performance of the preamble may beimproved to increase the probability of success of random access, but byblocking channel access of other UEs, the probability of success ofrandom access of other UEs may be reduced. Therefore, when transmittingmultiple PRACH preambles, it is necessary to change a multiple PRACHpreamble transmission method in consideration of a preamble performanceof a UE transmitting the multiple PRACH preambles and the probability ofsuccess of the channel access procedure of other UEs.

Accordingly, in various embodiments of the disclosure, in an basestation and UE configured to receive or transmit a PDSCH or a PUSCH inan unlicensed band, when the UE intends to perform random access, amethod of transmitting multiple PRACH preambles is proposed. Morespecifically, a method and device for improving a preamble performanceof the UE or the probability of success of a channel access procedure ofother UEs as the UE changes the channel access procedure methodaccording to the number of multiple PRACH preamble transmissions areproposed.

Hereinafter, the method and device proposed in the embodiments of thedisclosure are not limitedly applied to each embodiment, and will bepossible to utilize in a method and device for configuring ordetermining multiple PRACH preamble transmission using all or acombination of one or more embodiments proposed by the disclosure.Further, in an embodiment of the disclosure, a case in which the UEtransmits a PRACH preamble during a random access process will bedescribed as an example, but it will be applicable to a case in whichthe UE transmits multiple PUSCHs or PUCCHs, a case in which the basestation transmits multiple PDSCHs or PDCCHs, or a case of transmittingmultiple physical sidelink shared channels (PSSCH) or physical sidelinkcontrol channels (PSCCH) between UEs. Further, in the embodiment of thedisclosure, the description will be made on the assumption of an basestation and UE operating in an unlicensed band, but a method and deviceproposed in the embodiment of the disclosure may be applied even to anbase station and UE operating in a licensed band or a shared spectrum aswell as an unlicensed band.

Embodiment 1

In the present embodiment, in an base station and UE operating in anunlicensed band, when the UE transmits multiple PRACH preambles, amethod of configuring a channel access procedure gap is proposed. Inparticular, a method of increasing a length of a PRACH preambletransmission interval according to the number of PRACH preambletransmissions is proposed.

An operation of the embodiment will be described with reference to FIG.7 as follows.

In an base station and UE transmitting and receiving signals in anunlicensed band, it is assumed that the UE is configured to transmitmultiple PRACH preambles. In order to transmit a PRACH preamble at PRACHoccasions 704, 707, 710, and 713 indicated by higher layer signaling ordownlink control information, a UE 1 performs a channel access procedureat channel access procedure gaps 702, 705, 708, and 711 until a timepoint immediately before transmission of the PRACH preamble. As anexecution result of the channel access procedure, the UE 1 may transmita PRACH preamble at all PRACH occasions determined to an idle band.

When a first PRACH preamble 726 of the UE 1 is transmitted before atransmission possible time of a first PRACH preamble 730 of a UE 2 dueto transmission delay of the UE 2, after performing a channel accessprocedure 702 for transmission of the first PRACH preamble 726, the UE 1may determine that it is in an idle band to transmit the first PRACHpreamble 726. However, the UE 2 determines that it is not in an idleband as an execution result of a channel access procedure 714 due totransmission of the first PRACH preamble 726 of the UE 1 and cannottransmit the first PRACH preamble 730. In FIG. 7, when all gaps of thechannel access procedure performed by the UE 1 and the UE 2 are thesame, the UE 2 cannot transmit a PRACH preamble due to transmission ofmultiple PRACH preambles by the UE 1.

In order to protect the UE 2 from performing the channel accessprocedure, the UE 1 may reduce a cyclic prefix (CP) length of the PRACHpreamble according to the number of multiple PRACH transmissions. Forexample, when the UE 1 transmits the first PRACH preamble 726 and thenreduces a CP length 706 of a second PRACH preamble 727, a channel accessprocedure gap 705 to be performed for transmission of the second PRACHpreamble 727 becomes longer. However, in the case of the UE 2, because achannel access procedure gap 717 performed for transmission of a secondPRACH preamble 719 is the same as the previous channel access proceduregap 714, the probability of accessing the channel increases. Similarly,when the above-described method is equally applied to the second PRACHpreamble transmission of the UE 2, third PRACH preamble transmission 732of the UE 2 fails, and third PRACH preamble transmission 728 of the UE 1may succeed. Accordingly, both the UE 1 and the UE 2 may performmultiple PRACH preamble transmission. A more specific method ofadjusting a CP length of the PRACH preamble is as follows.

Method 1-1: Method of Reducing a CP Length Based on a Setup Value

The method 1-1 is a method in which the UE reduces a CP length accordingto the number of multiple PRACH preamble transmissions based on a presetvalue or rule with higher layer signaling or control information. Forexample, when the base station instructs the UE to transmit multiplePRACH preambles, the UE may reduce the CP length by a multiple of 1/Xaccording to the number of PRACH preamble transmissions, and themultiple value may be included in higher layer signaling or controlinformation to be configured to the UE by the base station. As anothermethod, the base station may configure an offset value of the CP lengthto the UE. In other words, when the base station configures the offsetvalue to X, the UE may reduce the CP length by X according to the numberof PRACH preamble transmissions to transmit the PRACH preamble. The Xvalue in the above two schemes may be configured by the base station tothe UE to one value using higher layer signaling or control information,may configure a value according to the number of PRACH preambletransmissions to a set (e.g., {X, Y, Z, T}), or may be configured to apredetermined rule (e.g., X, 2X, 3X, 4X) according to PRACH preambletransmission.

Method 1-2: Method of Reducing a Random Value-Based CP Length

The method 1-2 is a method in which the UE randomly selects a multipleor offset X value in the method 1-1 from a candidate group set by thebase station. For example, when the base station instructs a set (e.g.,{a, b, c, d}) of a multiple or offset value to the UE with higher layersignaling or control information, the UE may randomly extract a valuewithin a preset set when transmitting a PRACH to reduce the CP length.In this case, the UE may extract a value when transmitting each PRACHpreamble or apply the same value when transmitting each PRACH preambleafter extracting once.

Embodiment 2

In the present embodiment, in an base station and UE operating in anunlicensed band, when the UE transmits multiple PRACH preambles, amethod of configuring a channel access procedure gap is proposed. Inparticular, a method of increasing a channel access procedure gapaccording to the number of PRACH preamble transmissions is proposed.

An operation of the embodiment will be described with reference to FIG.8 as an example.

In an base station and UE transmitting and receiving signals in anunlicensed band, it is assumed that the UE is configured to performmultiple PRACH preamble transmission. In order to transmit a PRACHpreamble at a PRACH occasion indicated by higher layer signaling ordownlink control information, a UE 1 performs channel access procedures802, 804, 807, and 810 until a time point immediately beforetransmission of the PRACH preamble. As an execution result of a channelaccess procedure, the UE 1 may transmit a PRACH preamble for all PRACHoccasions determined to an idle band.

In order to protect the UE 2 from performing the channel accessprocedure, the UE 1 may increase a channel access procedure gapaccording to the number of multiple PRACH transmissions. For example,after transmitting a first PRACH preamble 803, the UE 1 may increase achannel access procedure gap 804 for transmitting a second PRACHpreamble 806. However, in the case of the UE 2, because a channel accessprocedure gap 815 performing for transmission of a second PRACH preamble816 is the same as a previous channel access procedure gap 813, theprobability of accessing the channel increases. Similarly, when theabove-described method is applied to second PRACH transmission of the UE2, third PRACH preamble transmission 819 of the UE 2 fails, and thirdPRACH preamble transmission 809 of the UE 1 may succeed. Accordingly,both the UE 1 and the UE 2 may perform multiple PRACH transmission. Inthis case, the UE may adjust the PRACH preamble length by the adjustedchannel access procedure gap. The UE may adjust the CP length of thePRACH preamble using a puncturing or rate matching method by theadjusted length, and perform a channel access procedure until a timepoint immediately before transmission of the PRACH preamble. A morespecific method of adjusting the channel access procedure gap is asfollows.

Method 2-1: Method of Increasing a Contention Window Value or Size

The method 2-1 is a method in which the UE increases a contention windowvalue or size according to the number of PRACH preamble transmissions.For example, assuming that the UE performs a channel access procedurewith a priority class 3 (p=3) of the above-described type1 for PRACHpreamble transmission and that a value (CW_p) of the contention windowused for transmitting the first PRACH preamble is 15, the UE configuresthe contention window value of the channel access procedure performedfor transmitting the second PRACH preamble to 31, which is the nextvalue. For this reason, the channel access procedure gap fortransmitting the second PRACH preamble by the UE probabilisticallyincreases.

Method 2-2: Method of Adjusting a Selection Gap of the Counter N Value

As described above, N is selected as an arbitrary integer value amongvalues between 0 and a value (CW_p) of a contention window at a timepoint that performs the channel access procedure. In the method 2-2,when a channel access procedure is performed according to the number ofPRACH preamble transmissions of the UE, a gap of selecting an N valuemay be adjusted. For example, assuming that the N value between 0 andCW_p used when performing the channel access procedure for transmittingthe first PRACH preamble by the UE is X, the UE may select the N valueas an integer value between X and CW_p when performing the channelaccess procedure for transmitting the second PRACH preamble. Therefore,the channel access procedure gap for transmitting the second PRACHpreamble by the UE increases.

Method 2-3: Method of Increasing the Length or Number of Sensing SlotsBased on a Setup Value

The method 2-3 is a method in which the UE increases the number (orlength) of sensing slots according to the number of multiple PRACHpreamble transmissions based on a preset value or rule with higher layersignaling or control information. For example, when the base stationinstructs the UE to transmit multiple PRACH preambles, the UE mayincrease the number (or length) of sensing slots by a multiple of Xaccording to the number of PRACH preamble transmissions, and themultiple value may be included in the higher layer signaling or controlinformation and be configured by the base station to the UE. As anothermethod, the base station may configure an offset value of the number (orlength) of sensing slots to the UE. In other words, when the basestation configures the offset value to X, the UE may increase the number(or length) of sensing slots by X according to the number of PRACHpreamble transmissions to perform a channel access procedure. The Xvalue in the above two methods may be configure by the base station tothe UE to one value using higher layer signaling or control information,may configure a value according to the number of PRACH preambletransmissions to a set (e.g., {X, Y, Z, T}), or may be configured to apredetermined rule (e.g., X, 2X, 3X, 4X) according to PRACH preambletransmission. Further, Method 3 may be applied to the type1 or type2channel access procedure.

Method 2-4: Method of Increasing a Random Value-Based Sensing SlotLength

The method 2-4 is a method in which the UE randomly selects a multipleor offset X value in the method 2-3 from a candidate group set to thebase station. For example, when the base station instructs a set (e.g.,{a, b, c, d}) of a multiple or offset value to the UE with higher layersignaling or control information, the UE may randomly increase a valuewithin the preset set by the number (or length) of sensing slots whentransmitting the PRACH. In this case, the UE may extract a value whentransmitting each PRACH preamble or apply the same value whentransmitting each PRACH preamble after extracting once.

Embodiment 3

In the present embodiment, in an base station and UE operating in anunlicensed band, when the UE transmits multiple PRACH preambles, amethod of configuring a channel access procedure gap is proposed. Inparticular, a method of reducing a length of a PRACH preambletransmission interval according to the number of PRACH preambletransmissions is proposed.

An operation of the embodiment will be described with reference to FIG.9 as follows.

In an base station and UE transmitting and receiving signals in anunlicensed band, it is assumed that the UE is configured to performmultiple PRACH preamble transmission. In order to transmit a PRACHpreamble at PRACH occasions 904, 907, 910, and 913 indicated by higherlayer signaling or downlink control information, a UE 1 performs channelaccess procedures 902, 905, 908, and 911 until a time point immediatelybefore PRACH preamble transmission. As an execution result of a channelaccess procedure, a UE 1 may transmit a PRACH preamble for all PRACHoccasions determined to an idle band.

In embodiments 1 and 2, because both the UE 1 and a UE 2 enable multiplePRACH preamble transmission, it may be efficient in terms ofcoexistence, but the random access success probability of the UE 1 maybe reduced; thus, technique that improves the random access successprobability of the UE 1 is needed.

In order to increase the probability of success in performing thechannel procedure of the UE 1, the UE 1 may increase a cyclic prefix(CP) length of the PRACH preamble according to the number of multiplePRACH transmissions. For example, when the UE 1 transmits a first PRACHpreamble 926 and then increases a CP length 906 of a second PRACHpreamble 927, a channel access procedure gap 905 to be performed fortransmission of the second PRACH preamble 927 is reduced. However, inthe case of the UE 2, because a channel access procedure gap 917performed for transmission of a second PRACH preamble 919 is the same asa previous channel access procedure gap 914, the probability ofaccessing the channel is further reduced. Similarly, when theabove-described method is applied to third PRACH preamble transmissionof the UE 1, the probability of third PRACH preamble transmission 928 ofthe UE 1 may further increase. Accordingly, the UE 1 may performmultiple PRACH preamble transmission at all possible PRACH occasions904, 907, 910, and 913. A more specific method of adjusting a CP lengthof the PRACH preamble is as follows.

Method 3-1: Method of Increasing a CP Length Based on a Setup Value

The method 3-1 is a method in which the UE increases a CP lengthaccording to the number of multiple PRACH preamble transmissions basedon a preset value or rule with higher layer signaling or controlinformation. For example, when the base station instructs the UE totransmit multiple PRACH preambles, the UE may increase the CP length bya multiple of 1/X according to the number of PRACH preambletransmissions, and the multiple value may be included in higher layersignaling or control information to be configured to the UE by the basestation. As another method, the base station may configure an offsetvalue of the CP length to the UE. In other words, when the base stationconfigures the offset value to X, the UE may increase the CP length by Xaccording to the number of PRACH preamble transmission to transmit thePRACH preamble. The X value in the above two techniques may beconfigured by the base station to the UE to one value using higher layersignaling or control information, may configure a value according to thenumber of PRACH preamble transmissions to a set (e.g., {X, Y, Z, T}), ormay be configured to a predetermined rule (e.g., X, 2X, 3X, 4X)according to PRACH preamble transmission.

Method 3-2: Method of Increasing a Random Value-Based CP Length

The method 3-2 is a method in which the UE randomly selects a multipleor offset X value in method 3-1 from a candidate group set by the basestation. For example, when the base station instructs a set (e.g., {a,b, c, d}) of a multiple or offset value to the UE with higher layersignaling or control information, the UE may randomly extract a valuewithin a preset set when transmitting the PRACH to increase the CPlength. In this case, the UE may extract a value when transmitting eachPRACH preamble or apply the same value when transmitting each PRACHpreamble after extracting once.

Embodiment 4

In the present embodiment, in an base station and UE operating in anunlicensed band, when the UE transmits multiple PRACH preambles, amethod of configuring a channel access procedure gap is proposed. Inparticular, a method of reducing a channel access procedure gap in orderto improve a random access success probability of the UE according tothe number of PRACH preamble transmissions is proposed.

An operation of the embodiment will be described with reference to FIG.9 as follows.

In order to increase the probability of success of the UE 1 performing achannel procedure, the UE 1 may reduce the channel access procedure gapaccording to the number of multiple PRACH transmissions. For example,after transmitting a first PRACH preamble 926, the UE 1 may reduce achannel access procedure gap 905 for transmitting a second PRACHpreamble 927. However, in the case of the UE 2, because a channel accessprocedure gap 917 performing for transmission of a second PRACH preamble919 is the same as a previous channel access procedure gap 914, theprobability of accessing the channel decreases. Similarly, when theabove-described method is applied to third PRACH preamble transmissionof the UE 1, the probability of third PRACH preamble transmission 928 ofthe UE 1 may further increase.

Accordingly, the UE 1 may perform multiple PRACH preamble transmissionin all possible PRACH occasions 904, 907, 910, and 913. In this case,the UE may adjust the PRACH preamble length by the adjusted channelaccess procedure gap. The UE may adjust the CP length of the PRACHpreamble using a puncturing or rate matching method by the adjustedlength, and perform a channel access procedure until a time pointimmediately before transmission of the PRACH preamble. A more specificmethod of adjusting the channel access procedure gap is as follows.

Method 4-1: Method of Reducing a Contention Window Value or Size

The method 4-1 is a method in which the UE decreases a contention windowvalue or size according to the number of PRACH preamble transmissions.For example, assuming that a channel access procedure is performed witha priority class 3 (p=3) of the above-described type1 for transmissionof a UE PRACH preamble and that a contention window value (CW_p) usedfor transmitting the first PRACH preamble is 31, the contention windowvalue of the channel access procedure performed by the UE fortransmitting a second PRACH preamble may be configured to 15, which is aprevious value. For this reason, the channel access procedure gap fortransmitting the second PRACH preamble by the UE probabilisticallydecreases. Further, it is also possible to use the same value of thecontention window used for transmission of the first PRACH preamble.

Method 4-2: Method of Adjusting a Selection Gap of the Counter N Value

As described above, N is selected as an arbitrary integer value amongvalues between 0 and a value (CW_p) of a contention window at the timepoint that performs the channel access procedure. In the method 4-2,when performing the channel access procedure according to the number ofPRACH preamble transmissions of the UE, a gap for selecting an N valuemay be adjusted. For example, assuming that the N value between 0 andCW_p used when performing the channel access procedure for transmittingthe first PRACH preamble by the UE is X, the UE may select the N valueas an integer value between 0 and X when performing a channel accessprocedure for transmitting a second PRACH preamble. Accordingly, the UEdecreases the channel access procedure gap for transmitting the secondPRACH preamble. Further, it is also possible to use the same N valueused for transmission of the first PRACH preamble.

Method 4-3: Method of Reducing the Length or Number of Sensing SlotsBased on a Setup Value

The method 4-3 is a method in which the UE reduces the number (orlength) of sensing slots according to the number of multiple PRACHpreamble transmissions based on a preset value or rule with higher layersignaling or control information. For example, when the base stationinstructs the UE to transmit multiple PRACH preambles, the UE may reducethe number (or length) of sensing slots by a multiple of X according tothe number of PRACH preamble transmissions, and the multiple value maybe included in higher layer signaling or control information and beconfigured by the base station to the UE. As another method, the basestation may configure an offset value of the number (or length) ofsensing slots to the UE. In other words, when the base stationconfigures the offset value to X, the UE may reduce the number (orlength) of sensing slots by X according to the number of PRACH preambletransmissions to perform a channel access procedure. The X value in theabove two methods may be configured by the base station to the UE to onevalue using higher layer signaling or control information, may configurea value according to the number of PRACH preamble transmissions to a set(e.g., {X, Y, Z, T}), or may be configured to a predetermined rule(e.g., X, 2X, 3X, 4X) according to PRACH preamble transmission. Further,the method 3 may be applied to the type1 or type2 channel accessprocedure.

Method 4-4: Method of Reducing a Random Value-Based Sensing Slot Length

The method 4-4 is a method in which the UE randomly selects a multipleor offset X value in the method 4-3 from a candidate group set by thebase station. For example, when the base station instructs a set (e.g.,{a, b, c, d}) of a multiple or offset value to the UE with higher layersignaling or control information, the UE may randomly reduce a valuewithin a preset set by the number (or length) of sensing slots whentransmitting the PRACH. In this case, the UE may extract a value whentransmitting each PRACH preamble or apply the same value whentransmitting each PRACH preamble after extracting once.

Embodiment 5

In the present embodiment, in an base station and UE operating in anunlicensed band, a method in which the base station instructs the UE totransmit multiple PRACH preambles is proposed.

Method 5-1: Instruct Multiple PRACH Preamble Transmission Using HigherLayer Signaling

In order to transmit multiple PRACH preambles in an unlicensed band, itis necessary to configure a gap for performing a channel accessprocedure in addition to the existing PRACH occasion setup. To this end,the base station may instruct the UE to transmit multiple PRACHpreambles with higher layer signaling. More specifically, the basestation may instruct the UE to transmit multiple PRACH preambles byseparate multiple PRACH configurations. For example, when a setup valueis absent or disabled (or a specific bit value, for example, 0), the UEperforms the existing PRACH preamble transmission. When the setup valueis enabled (or a specific bit value, for example, 1), the UE may performa channel access procedure between every PRACH occasion and performmultiple PRACH preamble transmission. In this case, the base station mayindicate a channel access procedure execution period (e.g., the X numberof OFDM symbols) between each PRACH occasion with separate higher layersignaling, or may determine multiple PRACH configurations, asillustrated in Table 4.

TABLE 4 Multiple PRACH configuration Contents ‘absent’ Existing PRACHpreamble transmission method Specific value (e.g, 0) Multiple PRACHpreamble transmission, or 1 OFDM (or Y us) channel access procedure gap= 1 OFDM symbol (or Y us) Specific value (e.g., 1) Multiple PRACHpreamble transmission, or 2 OFDM (or Z us) channel access procedure gap= 2 OFDM symbol (or Z us)

As another method, by adding Y bits to an existing PRACH configurationindex, the base station may instruct multiple PRACH preambletransmission. For example, when a last Y or first Y bit of the PRACHconfiguration index is a specific value (e.g., all 0), the UE performsthe existing PRACH preamble transmission, and when a last Y or first Ybit of the PRACH configuration index is another specific value (e.g.,all 1), the UE may perform a channel access procedure between everyPRACH occasion and perform multiple PRACH preamble transmission. In thiscase, the base station may indicate a channel access procedure executionperiod (e.g., X OFDM symbol length) between each PRACH occasion withseparate higher layer signaling or may determine a last Y or first Y bitin the PRACH configuration index, as illustrated in Table 2. As anothermethod, a PRACH configuration index for multiple PRACH preambletransmission may be additionally introduced. For example, PRACHconfiguration indices 0 to 255 may be used for configuring an existingPRACH occasion, and 256 to X (e.g., X=511) may be newly defined formultiple PRACH preamble transmission and PRACH occasion setup for themultiple PRACH preamble transmission. Here, the PRACH occasion may bevariously considered by reflecting a channel access procedure gap, apreamble format, or a PRACH occasion.

Method 5-2: Instruct Multiple PRACH Preamble Transmission Using DCI

The base station may instruct the UE to transmit multiple PRACHpreambles using DCI. In this case, the base station may indicate a gap(e.g., the number X of OFDM symbols) for multiple PRACH preambletransmission or channel access procedure to the UE through bitsignaling. In DCI, when the multiple PRACH preamble transmissionindicator is empty or indicates a specific value (e.g., 0), the UEperforms an existing PRACH preamble transmission scheme. When themultiple PRACH preamble transmission indicator of the DCI indicatesanother specific value (e.g., 1), the UE sets a gap (e.g., OFDM symbolX) for performing a channel access procedure between every preset PRACHoccasion with higher layer signaling. The gap (e.g., OFDM symbol X) forperforming the channel access procedure may be configured using aseparate indicator in DCI, or may indicate the number of symbols with avalue of the PRACH preamble transmission indicator, as illustrated inTable 5.

TABLE 5 Multiple PRACH preamble transmission indicator (bit) Contents 00(or absent) Basic operation 01 Multiple PRACH preamble transmission,channel access procedure gap = 1 OFDM symbol (or Y us) 10 Multiple PRACHpreamble transmission, channel access procedure gap = 2 OFDM symbol (orZ us) 11 Reserved

The above-described first to fifth embodiments are for convenience ofdescription, and each embodiment or methods proposed in each embodimentmay be implemented in combination.

An operation of an base station according to an embodiment of thedisclosure will be described with reference to FIG. 10 as follows.

The base station may transmit higher signal setup for initial access anda synchronization signal to the UE in step 1000. For example, signalssuch as a PSS, SSS, or PBCH may be transmitted to the UE, and a PDCCHresource region for initial access or CORESET setup, search spaceconfiguration information, and the like may be transmitted to the UEthrough a higher signal. In step 1010, the base station may additionallytransmit higher signal configuration, such as a random access-relatedPRACH configuration index, a frequency domain resource, RAR windowconfiguration information, and transmission power configurationinformation, to the UE. Further, the base station may transmit highersignal configuration related to multiple PRACH preamble transmission tothe UE. For example, in the first to fifth embodiments, information tobe configured to the UE for multiple PRACH transmission may betransmitted to the UE through a higher signal. A detailed descriptionthereof refers to information set with a higher signal in eachembodiment. In step 1020, the base station may transmit multiple PRACHpreamble transmission configuration information to the UE using DCI.When the PRACH transmission configuration information is transmittedwith a higher signal, step 1020 may be omitted. In step 1030, the basestation may detect a PRACH preamble at a PRACH occasion set to the UE.For example, according to at least one of the methods described in thefirst to fifth embodiments, the UE may transmit a PRACH preamble, andthe base station may detect the PRACH preamble. Subsequent operationsrefer to the random access procedure of FIG. 5.

A UE operation according to an embodiment of the disclosure will bedescribed with reference to FIG. 11 as follows.

In step 1100, the UE establishes synchronization with the base stationusing a synchronization signal, and receives configuration for initialaccess from the base station through a higher signal. PDCCH and PDSCHtransmission/reception are configured according to the receivedconfiguration information. For example, the UE may receive a downlinkPDCCH resource region or CORESET configuration, a search spaceconfiguration, and the like from the base station through a highersignal.

In step 1110, the UE may receive a higher signal related to randomaccess and multiple PRACH preamble transmission from the base station.In this case, the UE may receive a higher signal related to multiplePRACH preamble transmission using DCI. For example, in the first tofifth embodiments, information to be configured to the UE for multiplePRACH transmission may be transmitted to the UE through a higher signal.A detailed description thereof refers to information set with a highersignal in each embodiment.

If multiple PRACH preamble transmission is not configured in step 1120,the UE performs PRACH preamble transmission according to an existingmethod in step 1130.

If multiple PRACH preamble transmission is configured in step 1120, theUE performs a channel access procedure configured by the base stationand performs multiple PRACH preamble transmission in step 1140. Forexample, the UE may transmit a PRACH preamble and the base station maydetect the PRACH preamble according to at least one of the methodsdescribed in the first to fifth embodiments. Subsequent operations referto the random access procedure of FIG. 5.

FIG. 12 is a diagram illustrating a configuration of an base stationaccording to an embodiment of the disclosure.

As illustrated in FIG. 12, the base station of the disclosure mayinclude an base station receiver 1200, an base station transmitter 1210,and an base station processor 1220. The base station receiver 1200 andthe base station transmitter 1210 may be collectively referred to as atransceiver in an embodiment of the disclosure. The transceiver maytransmit and receive signals to and from the UE. The signal may includecontrol information and data. To this end, the transceiver may includean RF transmitter that up-converts and amplifies a frequency of atransmitted signal, and an RF receiver that amplifies a received signalwith low noise and that down-converts a frequency thereof. Further, thetransceiver may receive a signal through a wireless channel, output thesignal to the base station processor 1220, and transmit the signaloutput from the UE processor 1220 through the wireless channel. The basestation processor 1220 may control a series of processes so that thebase station may operate according to the above-described embodiment ofthe disclosure. For example, the base station receiver 1200 may receivea data signal including a control signal transmitted from the UE and apreamble signal for initial access, and the base station processor 1220may determine the reception result of a control signal and a data signalor a preamble signal transmitted by the UE. For another example, thebase station processor 1220 may perform a channel access procedure foran unlicensed band. For a specific example, the base station receiver1200 may receive signals transmitted in the unlicensed band, and thebase station processor 1220 may compare the strength of the receivedsignal with a threshold value defined in advance or determined by avalue of a function that takes a bandwidth as a factor to determinewhether the unlicensed band is in an idle state. For example, the basestation processor 1220 may control to transmit configuration informationfor transmission of multiple random access preambles to the UE, toreceive a first random access preamble from the UE based on theconfiguration information for transmission of the multiple random accesspreambles, and to receive a second random access preamble from the UE.In this case, at least one of a length of a channel access procedure gapfor the second random access preamble or a length of a random accesschannel transmission interval may be adjusted based on transmission ofthe first random access preamble. Adjusting the length of the randomaccess channel transmission interval includes adjusting a length of acyclic prefix (CP) related to the second random access preamble, and thebase station processor 1220 may configure at least one of a firstparameter indicating a multiple for adjusting a length of the CP to theUE or a second parameter indicating offset. Adjusting the length of thechannel access procedure gap includes adjusting contention windowrelated information or a sensing slot, and the base station processor1220 may configure at least one of a contention window value, a counterN value, a size of the sensing slot, or a length of the sensing slot tothe UE. Further, the base station processor 1220 may provide informationindicating a symbol length of the channel access procedure gap andtransmission of the multiple random access preambles to the UE, and themultiple random access preambles may be received in an unlicensed band.

The base station processor 1220 may be defined to a controller andinclude at least one processor.

FIG. 13 is a diagram illustrating a configuration of a UE according toan embodiment of the disclosure.

As illustrated in FIG. 13, the UE of the disclosure may include a UEreceiver 1300, a UE transmitter 1310, and a UE processor 1320. The UEreceiver 1300 and the UE transmitter 1310 may be collectively referredto as a transceiver in an embodiment of the disclosure. The transceivermay transmit and receive signals to and from the base station. Thesignal may include control information, data, and a preamble. To thisend, the transceiver may include an RF transmitter that up-converts andamplifies a frequency of a transmitted signal, and an RF receiver thatamplifies a received signal with low noise and that down-converts afrequency thereof. Further, the transceiver may receive a signal througha wireless channel, output the signal to the UE processor 1320, andtransmit a signal output from the UE processor 1320 through a wirelesschannel. The UE processor 1320 may control a series of processes so thatthe UE may operate according to the above-described embodiment of thedisclosure. For example, the UE receiver 1300 may receive a data signalincluding a control signal, and the UE processor 1320 may determine areception result of the data signal. Thereafter, when the first signalreception result including the data reception should be transmitted tothe base station at the timing, the UE transmitter 1310 transmits thefirst signal reception result to the base station at the timingdetermined by the processor. For another example, when the UE receiver1300 receives information on multiple PRACH preamble transmission fromthe base station, the UE processor 1320 may reset or change a channelaccess procedure gap or a CP length of the PRACH preamble according tothe number of PRACH transmissions of the UE; thus, the UE transmitter1310 may transmit the PRACH preamble. The UE processor 1320 may controlto receive configuration information for transmission of multiple randomaccess preambles from the base station, transmit a first random accesspreamble based on the configuration information for transmission of themultiple random access preambles, to adjust at least one of a length ofa channel access procedure gap or a length of a random access channeltransmission interval for a second random access preamble based ontransmission of the first random access preamble, and to attempt channelaccess for the second random access preamble transmission in the channelaccess procedure gap based on adjustment of at least one of the lengthof the channel access procedure gap or the length of the random accesschannel transmission interval. Adjusting the length of the random accesschannel transmission interval includes adjusting a length of a cyclicprefix (CP) related to the second random access preamble, and at leastone of a first parameter indicating a multiple for adjusting the lengthof the CP from the base station or a second parameter indicating theoffset may be configured. Adjusting the length of the channel accessprocedure gap includes adjusting contention window related informationor a sensing slot, and at least one of a contention window value, acounter N value, a size of the sensing slot, or a length of the sensingslot may be configured by the base station. The UE processor 1320 maycontrol to obtain information indicating transmission of the multiplerandom access preambles and a symbol length of the channel accessprocedure gap from the base station, and to transmit the multiple randomaccess preambles in an unlicensed band.

The UE processor 1320 may be defined to a controller and include atleast one processor.

The embodiments of the disclosure disclosed in the present specificationand drawings are only provided for specific examples to easily describethe technical content of the disclosure and to help understanding of thedisclosure, and are not intended to limit the scope of the disclosure.That is, it is apparent to those of ordinary skill in the art that othermodifications based on the technical idea of the disclosure can beimplemented. Further, each of the above embodiments may be combined andoperated as necessary. For example, some of the methods proposed in thedisclosure may be combined with each other to operate an base stationand a UE. Further, although the above embodiments have been presentedbased on 5G and NR systems, other modifications based on the technicalidea of the above embodiment may be implemented in other systems such asLTE, LTE-A, and LTE-A-Pro systems.

1. A method performed by a terminal, the method comprising: receivingconfiguration information for transmission of multiple random accesspreambles from a base station; transmitting a first random accesspreamble based on the configuration information for transmission of themultiple random access preambles; adjusting at least one of a length ofa channel access procedure gap for a second random access preamble or alength of a random access channel transmission interval based ontransmission of the first random access preamble; and attempting channelaccess for transmission of the second random access preamble in thechannel access procedure gap based on adjustment of at least one of thelength of the channel access procedure gap or the length of the randomaccess channel transmission interval.
 2. The method of claim 1, whereinadjusting the length of the random access channel transmission intervalincludes adjusting a length of a cyclic prefix (CP) related to thesecond random access preamble, and wherein at least one of a firstparameter indicating a multiple for adjusting the length of the CP or asecond parameter indicating offset is configured by the base station. 3.The method of claim 1, wherein adjusting the length of the channelaccess procedure gap includes adjusting contention window relatedinformation or a sensing slot, and wherein at least one of a contentionwindow value, a counter N value, a size of the sensing slot, or a lengthof the sensing slot is configured by the base station.
 4. The method ofclaim 1, wherein information indicating transmission of the multiplerandom access preambles and a symbol length of the channel accessprocedure gap is obtained from the base station, and wherein themultiple random access preambles are transmitted in an unlicensed band.5. A terminal, comprising: a transceiver; and a controller configuredto: receive configuration information for transmission of multiplerandom access preambles from a base station through the transceiver,transmit a first random access preamble based on the configurationinformation for transmission of the multiple random access preamblesthrough the transceiver, adjust at least one of a length of a channelaccess procedure gap or a length of a random access channel transmissioninterval for a second random access preamble based on transmission ofthe first random access preamble, and attempt channel access fortransmission of the second random access preamble in the channel accessprocedure gap based on adjustment of at least one of the length of thechannel access procedure gap or the length of the random access channeltransmission interval.
 6. The terminal of claim 5, wherein adjusting thelength of the random access channel transmission interval includesadjusting the length of a cyclic prefix (CP) related to the secondrandom access preamble, and wherein at least one of a first parameterindicating a multiple for adjusting the length of the CP or a secondparameter indicating offset is configured by the base station.
 7. Theterminal of claim 5, wherein adjusting the length of the channel accessprocedure gap includes adjusting contention window related informationor a sensing slot, and wherein at least one of a contention windowvalue, a counter N value, a size of the sensing slot, or a length of thesensing slot is configured by the base station.
 8. The terminal of claim5, wherein information indicating transmission of the multiple randomaccess preambles and a symbol length of the channel access procedure gapis obtained from the base station, and wherein the multiple randomaccess preambles are transmitted in an unlicensed band.
 9. A methodperformed by a base station, the method comprising: transmittingconfiguration information for transmission of multiple random accesspreambles to a terminal; receiving a first random access preamble fromthe terminal based on the configuration information for transmission ofthe multiple random access preambles; and receiving a second randomaccess preamble from the terminal, wherein at least one of a length of achannel access procedure gap or a length of a random access channeltransmission interval for the second random access preamble is adjustedbased on transmission of the first random access preamble.
 10. Themethod of claim 9, wherein adjusting the length of the random accesschannel transmission interval includes adjusting a length of a cyclicprefix (CP) related to the second random access preamble, and wherein atleast one of a first parameter indicating a multiple for adjusting thelength of the CP or a second parameter indicating offset is configuredto the terminal.
 11. The method of claim 9, wherein adjusting the lengthof the channel access procedure gap includes adjusting contention windowrelated information or a sensing slot, and wherein at least one of acontention window value, a counter N value, a size of the sensing slot,or a length of the sensing slot is configured to the terminal.
 12. Themethod of claim 9, wherein information indicating transmission of themultiple random access preambles and a symbol length of the channelaccess procedure gap is provided to the terminal, and wherein themultiple random access preambles are received in an unlicensed band. 13.A base station, comprising: a transceiver; and a controller configuredto: transmit configuration information for transmission of multiplerandom access preambles to a terminal through the transceiver, receive afirst random access preamble from the terminal through the transceiverbased on the configuration information for transmission of the multiplerandom access preambles, and receive a second random access preamblefrom the terminal through the transceiver, wherein at least one of alength of a channel access procedure gap or a length of a random accesschannel transmission interval for the second random access preamble isadjusted based on transmission of the first random access preamble. 14.The base station of claim 13, wherein adjusting the length of the randomaccess channel transmission interval includes adjusting a length of acyclic prefix (CP) related to the second random access preamble, andwherein at least one of a first parameter indicating a multiple foradjusting the length of the CP or a second parameter indicating offsetis configured to the terminal.
 15. The base station of claim 13, whereinadjusting the length of the channel access procedure gap includesadjusting contention window related information or a sensing slot,wherein at least one of a contention window value, a counter N value, asize of the sensing slot, or a length of the sensing slot is configuredto the terminal, wherein information indicating transmission of themultiple random access preambles and a symbol length of the channelaccess procedure gap is provided to the terminal, and wherein themultiple random access preambles are received in an unlicensed band.